Laptop fan control Acer Travelmate 5760

I have Arch linux installed on my old Acer Travelmate 5760 and I was trying to software control the fan speed and status, but I can't find anything about the fan with lshw and lm-sensors and also the BIOS is quite old and doesn't have any fan option. I also tried NBFC and I can actually change the fan behavior but not really control or monitor its speed (there isn't the exact model configuration and with similar models the values are wrong and the effect is quite random). How the fan is actually controlled at low level? In the kernel? How can I get information on how the fan is controlled? Can I just read/write to some *file*, *register* or something similar to monitor/control it?